Now I understand what you were asking me. It is my belief that the head unit contains the amp (I have no idea what its power rating is). I'd be rather surprised if the head unit is a separate pre amp with a tuner. The only separate amp in the car that's depicted in the wiring schematics is the one powering the subs in the front doors.
As far as the door open shut off function is concerned, that is how the power to the amp is controlled with PAC Unit. If you turn off the ignition and leave the door closed, the amps stays on for that predetermined period. However, as soon as the door is opened, the power to the amp is switched off.